The Internet of Things (IoT) is a vision for the future world where everything that can benefit from a connection will be connected. Cellular technologies are being developed or evolved to play an indispensable role in the IoT world, particularly the machine type communication (MTC). MTC is characterized by lower demands on data rates than, for example, mobile broadband, but with higher requirements on, e.g., low cost device design, better coverage, and ability to operate for years on batteries without charging or replacing the batteries. To meet the IoT design objectives, Third Generation Partnership Project (3GPP) has standardized Narrowband IoT (NB-IoT) in Release (Rel) 13 that has a system bandwidth of 180 kilohertz (kHz) and targets improved coverage, long battery life, low complexity communication design, and network capacity that is sufficient for supporting a massive number of devices.
To further increase the market impact of NB-IoT, extending its deployment mode to unlicensed band operation is being considered. For example, in the United States of America (US), the 915 megahertz (MHz) and 2.4 gigahertz (GHz) Industrial, Scientific and Medical (ISM) bands may be considered. However, an unlicensed band has specific regulations to ensure different systems can co-exist in the band with good performance and fairness. This requires certain modifications to Rel-13 NB-IoT for it to comply with the regulations. In the aforementioned US ISM bands, it is advantageous to adopt frequency hopping (FH) so that a transmitter can transmit at a higher power level without power spectral density (PSD) limitation or requiring listen-before-talk (LBT). When FH is adopted, a User Equipment (UE) needs to learn the hopping pattern employed by the eNB of the cell before it can start actual communication.